The Role of Dopamine in the Control of Neurobiological Functions

Effects of prenatal and postnatal exposure to amitraz on norepinephrine, serotonin and dopamine levels in brain regions of male and female rats

The effects of maternal exposure to amitraz on brain region monoamine levels of male and female offspring rats at 60 days of age were observed. Maternal and offspring body weight, physical and general activity development were unaffected by the exposure of dams to amitraz (20mg/kgbw, orally on days 6-21 of pregnancy and 1-10 of lactation). Male and female offspring were sacrificed at 60 days of age and possible alterations in the content and metabolism of NE, DA and 5-HT were determined in brain regions by HPLC. The results showed that all these neurotransmitter systems were altered in a brain regional-related manner. In male and female offspring, amitraz induced a significant decrease in the prefrontal cortex 5-HT and its metabolite 5-HIAA and DA and its metabolites DOPAC and HVA levels with interaction of sex. Nevertheless, we verified that striatum DA and 5-HT and corresponding metabolite contents decreased in male and female offspring without statistical distinction of sex. In contrast, amitraz did not modify 5-HT content, but caused an increase in 5-HIAA content in the medulla oblongata and hippocampus in male and female offspring. Alterations in the hippocampus DA, DOPAC and HVA levels after amitraz exposure were also observed displaying a sex interaction. NE levels also showed a decrease after amitraz treatment in the prefrontal cortex and striatum without statistical sex interaction, but MHPG levels decreased in both regions with a sex interaction. Amitraz evoked increases in 5-HT turnover in the prefrontal cortex as well as in DA turnover in the striatum and hippocampus but decreases in NE turnover in the hypothalamus, prefrontal cortex and striatum. The present findings indicated that maternal exposure to amitraz altered noradrenergic, serotonergic and dopaminergic neurochemistry in their offspring in the prefrontal cortex, striatum and hippocampus, and those variations could be related to several alterations in the functions in which these brain regions are involved.

Cation requirements of basal and ATP-regulated dopamine transport in rat pheochromocytoma cells

The transport of dopamine into presynaptic nerve terminals is the primary mechanism for the termination of dopaminergic neurotransmission. This transport process has recently been found to be composed of two components, a basal dopamine transport pathway which exists in the absence of extracellular ATP and an ATP-regulated moiety which comprises approximately 66% of the total transport system [Cao C. J. et al. (1990) Biochem. Pharmac. 39, R9-R14; Cao C. J. et al. (1989) Biochemistry 8, 207-220; Dunigan C. D. and Shamoo A. E. (1995) Neuroscience 65, 1-4; Eshleman A. et al. (1995) Life Sci. 56, 1613-1621]. Using a rat pheochromocytoma cell line and a Krebs bicarbonate buffering system, the present study examined the effect of several cations on both basal and ATP-regulated dopamine transport. In the absence of extracellular ATP, dopamine transport had an absolute dependence on the presence of Na+, but exhibited no requirement for Mg2+. Kinetically, the addition of 120 mM NaCl increased the Vmax of basal dopamine transport by approximately 150%. In contrast, the ATP-regulated dopamine transport pathway displayed a different sensitivity to Na+ and was completely dependent upon the presence of Mg2+. The addition of 1.2 mM MgSO4 increased the Vmax of transport in the presence of 0.7 mM extracellular ATP by 222%. Both basal and ATP-regulated transport were unaffected by the removal of either Ca2+ or K+ from the assay buffer. When the effects of ouabain, a potent inhibitor of Na+, K(+)-ATPase, were tested in the rat pheochromocytoma cell model, it was found that concentrations of ouabain as high as 1 mM were ineffective at inhibiting either the basal or ATP-regulated dopamine transport components. These results imply that the Na+ gradient supplied by Na+, K(+)-ATPase is not the sole provider of energy needed to drive either transport process. The ionic requirements of the basal and ATP-regulated dopamine transport pathways demonstrate the distinction between the two transport processes. In addition, the ionic dependency profile of the ATP-regulated moiety has provided some mechanistic insights into ATP-regulated catecholamine uptake, as the absolute Mg2+ requirement and the ineffectiveness of Ca2+ argues against the involvement of either purinergic receptors or a Ca(2+)-dependent, Mg(2+)-independent ectokinase in the ATP-regulated transport system.

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Ultrastructural analysis of growth of Nocardia asteroides during invasion of the murine brain

BALB/c mice were infected with 10(6) CFU of log-phase cells of Nocardia asteroides GUH-2 by tail vein injection (at this lethal inoculum dose, approximately 800 to 1,000 CFU becomes deposited in the brain). At 24 h after infection, the ultrastructural interactions of the nocardiae during growth within the murine brain were investigated. The nocardiae grew perivascularly in the pons, substantia nigra, hypothalamus, and thalamus portions of the brain, where they were either within or associated with most brain cell types. There appeared to be a propensity for growth within the soma of neurons and their axonal extensions. The nocardial cells were surrounded by 1 to 30 layers of membrane, and the innermost membrane was usually tightly adherent to the cell wall. This compartmentalization of nocardiae within brain cells could contribute to their failure to induce an inflammatory response or a cytopathic effect. Nevertheless, the bacteria were able to obtain adequate nutrients from the host to grow within the brain. The nocardiae were not completely inert, since some of the brain cells showed signs of degeneration. The myelin sheaths of axons were the most strongly affected, and there was evidence of demyelinization and axonal degeneration. Nocardiae growing within brain cells were phagocytized by compact, dense cells that were probably microglia. There was no ultrastructural evidence that the nocardiae were damaged by these phagocytes 24 h after infection; nevertheless, these cells may be important for the elimination of nocardiae from the brain during a nonlethal infection.